WASHINGTON  Visitors to the Army's Web site on tank warfare won't find a single urban battle among 13 online practice scenarios. After all, for decades the Army rule for bringing tanks into cities to fight has been simple: Don't.

"In classic armored warfare, you bypass the cities," says Montgomery Meigs, retired Army general and 1991 Gulf War tank commander. Nearly invulnerable on the battlefield, tanks lose a lot of their advantage in urban fighting. "It's a completely different ballgame," Meigs says. The enemy "can get a lot closer to you, and he can get behind you and above you" to hit places where a tank's armor is thin.

But the insurgents of Iraq have forced U.S. tanks into Iraq's cities by choosing to fight there. Commanders consider the intimidation and firepower of the Abrams a crucial tool for putting down insurgents. When the Marines crushed insurgent-held Fallujah last fall, they brought in two extra brigades of Army M1 Abrams tanks. (Related story: Tanks take a beating in Iraq)

Despite billions spent to build Stryker light armored vehicles and add armor to Humvees, "the M1 tank is still the platform of choice," says Col. Russ Gold, a former commander in Iraq and chief of staff at the U.S. Army's Armor Center in Fort Knox, Ky. Gold's brigade fought from inside the Abrams every day in central Iraq. "Primarily it was the shock effect, and it provided a lot of protection."

The tank warfare of Iraq has changed the Army's mindset, in which heavy armor increasingly was considered something from a bygone era, says Lt. Col. Michael Flanagan, an armor officer and director of a rush program to refit the Abrams for urban combat.

"Before Operation Iraqi Freedom, the Army had one vision for the future: ... This notion that a lighter, more mobile force" would make armor obsolete. Now, the Army is recognizing that the tanks must be upgraded, he says, so their armor can be used even more effectively, especially in the cities.

The upgrades are needed because instead of facing against other tanks 2 miles away, for which the tank is well armored in front, soldiers face an enemy of foot soldiers who bury mines in the streets and fire rocket-propelled grenades from rooftops and alleyways.

"You have a threat that operates to the side and to the rear," he says. "Understandably, we've got some vulnerability."

Even during the initial invasion two years ago, the Iraqi resistance knew the weak spots on the Abrams. During the first "Thunder Runs" of U.S. armor into downtown Baghdad troops reported that Iraqi ambushers would wait for a tank to pass and then fire their rocket-propelled grenades at the tank's rear engine compartment en masse, sometimes a dozen or more at once, hoping for a disabling hit.

Today, the Abrams remains the most-prized target for insurgents, in large part because of the psychological value.

"To parade (a captured or damaged Abrams) through the streets of Baghdad would have been huge," says Col. John Shay, an Army tank developer. However, all the Abrams tanks damaged in Iraq have been recovered, he says.

"Nothing's invulnerable," Meigs says. He says the key to effective use of the Abrams is how it is used. By itself it can be hit, but it's much less likely when the Army is fighting with a combination of tanks, artillery, aircraft and infantry. "The enemy can't handle that."

The Abrams upgrade package, known as TUSK, for Tank Urban Survival Kit, includes:

• A shield for the external machine gun operated by the tank loader when the Abrams is on patrol.

• A new remote-controlled machine gun operated from inside the tank.

• A high-strength armored grate for the rear, to catch grenades and rockets and explode them before they can make a disabling hit.

• Side armor panels to better protect the treads, suspension and hydraulics.

• An external telephone so that foot soldiers working alongside the tank can talk to the crew inside.

The Army also has tested and is preparing to issue, for Iraq and Korea, a new round for the tank's main gun for close combat. Current rounds are either high explosive or armor-piercing shells. The new round turns the Abrams into a giant shotgun, blasting 1,100 tungsten pellets at a time out of its 120mm barrel.

Besides the equipment upgrades, the Armor training center at Fort Knox is emphasizing urban situations in its training, including use of the crew's machine guns and pistols against close-in enemies, Shay says.

Francisco Jardim, director of the Patton Museum, says the Abrams is a technical marvel. But there's a familiar ring to the upgrades.

The external telephone, the new side armor and the shotgun-like "canister round" all recall previous tanks and previous wars. Troops in World War II would put sandbags on their Sherman tanks to protect against Nazi infantry and their Panzerfaust anti-tank guns.

As much as the Army has desired through history to avoid them, "those cities have a pesky way of just popping up in the landscape," he says.